1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display capable of reducing a distortion of a common voltage.
2. Discussion of the Related Art
An active matrix type liquid crystal display displays a motion picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal display has been implemented in televisions as well as display devices in portable devices such as office equipments and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, a cathode ray tube (CRT) is being rapidly replaced by the active matrix type liquid crystal display.
In the active matrix type liquid crystal display, a data voltage is applied to pixel electrodes, and a common voltage is applied to common electrodes opposite the pixel electrodes. The common electrodes are commonly connected to panel common lines. Liquid crystal cells are driven by the voltages applied to the pixel electrodes and the common electrodes.
However, the common voltage is easily distorted by a deviation between resistances of the panel common lines or a deviation between the common voltages over the entire surface of a liquid crystal display panel based on a structure of the panel common lines. As shown in FIG. 1, because a common voltage Vcom is applied to a liquid crystal display panel through only two input positions of an upper portion of the liquid crystal display panel, it is difficult to hold the common voltage Vcom at a constant level over the entire surface of the liquid crystal display panel because of a load of panel common lines. Because the load of the panel common lines depends on an amount of RC delay defined by a multiplication of a resistance and a parasitic capacitance of the panel common lines, the load of the panel common lines increases as a distance between the panel common line and the input position increases. The deviation of the common voltage Vcom causes a difference between luminances of upper and lower portions of the liquid crystal display panel and a flicker, and also accumulates DC components inside the panel to thereby generate image sticking. Accordingly, line widths of the panel common lines have to increase so as to reduce the amount of RC delay. However, because an increase in the line widths of the panel common lines causes a reduction in an aperture ratio of the liquid crystal display panel, it is difficult to consider the increase in the line widths of the panel common lines.
The liquid crystal display has recently adopted a high speed driving method so as to prevent motion blur. In the high speed driving method, the common voltage Vcom is not kept constant and is affected by a scan pulse or a data voltage. Hence, a ripple phenomenon is generated in the common voltage Vcom. The ripple phenomenon of the common voltage Vcom generates a horizontal crosstalk when a specific data pattern is displayed on the screen.